A conveying system installed in an apparatus for manufacturing semiconductors can, for example, be mentioned as such an environment. If grease is used as a lubricant for a direct-acting bearing in such an environment, the evaporation of oily matter from the grease causes problems, such as a lowering of its lubricating property and the pollution of the environment.
In such an event, it has hitherto been usual to coat at least one of the track surface of a rail in the form of a shaft, or a cylindrical movable body, or the surfaces of rolling bodies with a film of a solid lubricant, such as a soft metal such as gold, silver, lead or copper, or carbon, or molybdenum disulfide. The coating film formed from a solid lubricant as stated above, however, comes off little by little with the rolling or sliding motions of the rolling bodies. This causes an amount of dust which is inadequate for, among others, a clean environment, though it is a smaller amount than when grease is used. The amount of dust which is formed increases particularly under a high load.
The application of this applicant has coated the components of a direct-acting bearing with a solid lubricant obtained by mixing a fluororesin with a binder, and has made it possible to reduce dusting drastically, as compared with the usual case described above.
Even this coating film, however, produces a large amount of dust by getting worn, as well as by peeling or chipping, and has a short dust-free life, if it is subjected to a relatively high radial load. Moreover, the peeling or chipping of the coating film decreases the life to the direct-acting bearing, since it has a lower lubricating effect on the rolling and sliding portions of the bearing and allows its components to stick together and become worn more easily as a result of metal to metal contact. If the environment contains a corrosive gas, it corrodes the components of the bearing in those portions thereof from which the coating film has peeled, or chipped.
It is, therefore, an object of the present invention to restrain dusting in a direct-acting bearing and improve its lubrication to enable it to have a long life.